The instant invention relates to actuation of vehicular safety devices and, more particularly, to a power rate process using the rate of power change in vehicle acceleration (deceleration) to determine crash severity and, hence, whether a vehicle safety device should be actuated or deployed.
A variety of systems for actuating vehicular safety devices are well known in the art. Such systems are used to sense a crash condition and, in response to such a condition, to actuate an air bag, or lock a seat belt, or actuate a pretensioner for a seat belt retractor. Typically, the safety device is actuated or deployed into its protective position when an impact exceeding a predetermined magnitude is detected by the actuating system.
One prior art method of crash detection integrates the output of an electronic acceleration sensor over time and compares the result against a threshold velocity. One problem with the integration method of crash detection is that the crash severity cannot be determined early enough for high-speed angular, partial barrier, or pole crashes. Moreover, the wide "grey area" between "fire" and "no-fire" conditions for low-speed crash conditions often results in an inadvertent deployment of the safety device when deployment is unnecessary, or a non-deployment of the safety device when deployment is necessary.
A second known method of crash detection using an electronic acceleration sensor attempts to deemphasize the use of simple velocity calculations and instead measures the energy dissipated during a crash to assess crash severity. However, this "energy method" still utilizes velocity information, resulting in the same types of deployment problems and slow response time as are encountered with the integration method. Additionally, the energy method has a further limitation of detection capability in that it is accurate only over short time intervals.
In an effort to provide improved crash detection capability, U.S. Pat. No. 3,762,495 to Usui et al discloses crash evaluation circuitry which concurrently employs both a jerk algorithm, indicative of rate of change of vehicle deceleration, and a deceleration algorithm, indicative of the level of vehicle deceleration. However, experience has shown that jerk alone is incapable of properly discriminating between conditions requiring actuation of a vehicle safety device and conditions where such actuation is either unnecessary or undesirable. And, since the Usui system requires simultaneous "fire" signals from its two evaluation circuits before the safety device is actuated, the Usui system continues to poorly discriminate between "fire" and "no fire" conditions.